Electron emitting body



June 17, 1941. GOQSKENS 7 2,246,131

- ELECTRON EMITTING BODY- Filed June 12, 1940 Fig. l.

Inventor: Henricus Gooskens,

by His ttorn e y.

long.

I Patented June 17, 1941 UNITED STATES PATENT. OFFICE ELECTRON EMITTING BODY Henricus. Gooskcns, Eindhoven, Netherlands, assignor to General Electric Company, a corporation of New York Application .lune'iz, 1940, Serial No. 340,162 In the Netherlands May 22, 1939' p 3 Claims.

The invention described and claimed herein relates to an electron-emitting body for use at high temperatures and comprises an improvement on prior application Serial No. 159,595,.

filed August 17,1937.

In the aforesaid application, emitting electrodes are described which are particularly suitable for use in gas-filled discharge devices adapted to operate at high pressures and-temperatures. glass-like emitting material which is built up from acidic and basic oxides, the basic component being present in excess. The particular oxides employed are all of such character that their boiling points lie above 2,000 deg. C. and

the boiling point of at least one of the basic components present in excess should, according to the invention described in the aforesaid ap-.

It is found that the emitting characteristics of a material such as that which is described above may be improved by'in corporating in the emitter a relatively large proportion of a metal of the class which consists of tungsten and molybdenum. The application of such metals in an emitting coating applied directly to a metallic base structure appears impractical, however, for

the reason that the rate of conduction of heat from the metal particles to the electrode structure becomes so high that the glow discharge initially formed will not readily change into an arc discharge when the emitter is used in gasfilled tubes. g

In accordance with our present invention this difiiculty is overcome by separating the emitter into two strata of which the first is of insulating character and is preferably provided-by a glasslike emitting composition of the character described in the aforesaid prior application Serial No. 159,595. The second layer which is applied as a superficial coating to the first, comprises tungsten or molybdenum mixed with a,-small quantity by weight of the glass-like emitter,

which then serves as 'a high temperature binder without in any way limiting the emission of the The electrodes are provided with a' combination. If desired, a quantity of alkaline earth material may be incorporated in the metallized coating. As a result of the fact that an insulating layer is provided between the metallized emitting surface of the electrode structure and the metallic body of the electrode, heat loss is minimized while, at the same time excellent emitting properties and long life are realized. It is found that evaporation of the outer layer of the emitting material is substantially negligible while the composite structure of the emitting coating permits a sufficient diffusion of electrons to occur to maintain the electrode surface continuously activated.

Referring particularly to Fig. 1 of the drawing, there is shown a high pressure mercury vapor discharge tube I, useful for the generation of light or of ultra violet rays. This tube, which is surrounded by a bulbous enclosure 2, is intended to operate with an internal mercury vapor pressure of at least more than five atmospheres.

'In order to sustain a discharge within the tube it is provided at each end with discharge electrodes as indicated at 3 and 3.

Each of the electrodes is heated exclusively by the discharge, and may consist, for example, of a tungsten wire on which another tungsten wire is helically coiled. 'The wires are covered with an emitting coating formed in the manner above described; that is, the surface of the base struc-' ture is coated with a layer of an insulating material constituted of the combination of a basic component provided by an oxide of the class consisting of zirconium, beryllium, lanthanum and thorium oxides and an acidic component provided by an oxide of the class consisting of silicon and aluminum oxides. On this insulating layer there is applied a metallized coating which paste obtained in this manner, which contains a large excess of tungsten, a uniform coating is applied superficially to the insulating layer I provided on the electrode core. Subsequently the electrode is heated to a temperature of approximately 2200 deg. C. ina reducing atmosphere,

for instance, in a mixture of nitrogen and hydrogen, and a glass-like mass consisting preponderantly of tungsten on the outside is obtained on the electrode.

The structure realized in this way is represented generally in Fig. 2 which constitutes a cross-section of a single filamentary element of the electrode 3 of Fig. 1 when the same is treated in the manner above specified. The illustration referred to shows that the metal core 6 is completely covered with an insulating layer 1 formed of a combination of acidic and basic oxides as above described. On the surface of this combination there is provided an externalcoating consisting of tungstenparticles 8 solidly embedded in a glass-like binder.

What I claim as new and desire to secure b Letters Patent of the United States is:

1. A cathode for use at high temperatures component provided by an oxide of the class consistmg of silicon and aluminum oxides, and a superficial coating on the said layer and covering substantially the entire active surface of the cathode, said coating comprising a fused mixture of a further quantity of the aforesaid glass-like material witha metallic constituent of the class consisting of tungsten and molybdenum.

2. A cathode for use at high temperatures comprising the combination of a. metallic base structure, a layer of a glass-like material on the base structure, said material comprising a fused mixture of thorium oxide and silicon oxide in which the thorium oxide is present in excess, and a coating on the said layer and covering substantially the entire active surface of the cathode,

said coating comprising a fused mixture of tungsten particles with a further quantity of the said insulating material.

3. A cathode according to claim 1 in which the said coating additionally contains a quantity of an alkaline earth material.

.HENRIQUS GOOSKENS. 

